ML18030B221

Responds to 851007 Request for Addl Info Re NUREG-0737,Item II.K.3.18, Mods to Automatic Depressurization Sys (ADS) Logic. No Design Basis Requirement or Increase in Safety Associated W/Requested ADS Logic Mod.Present ADS Adequate

ML18030B221
Person / Time
Site:	Browns Ferry
Issue date:	03/26/1986
From:	Gridley R TENNESSEE VALLEY AUTHORITY
To:	Muller D Office of Nuclear Reactor Regulation
Shared Package
ML18030B222	List: ML18030B221 ML18030B223
References
RTR-NUREG-0737, RTR-NUREG-737, TASK-2.K.3.18, TASK-TM NUDOCS 8604080228
Download: ML18030B221 (6)

Text

ACCESSION NBR FAC IL: 50-259 50-2ba.50-29b AUTH.NAME QRIDLEYi R.RECIP.NAME MULLER>D.R.I REGULATORY I RMATION DISTRIBUTION SYS (BIDS)8b04080228 DOC.DATE: 8b/03/2b NOTARIZED:

NO DOCKET 0 Browns Ferry Nuclear Power Station.Unit ii Tennessee 05000259 Browns Ferry Nuclear Power St'ationi Unit 2E Tennessee 050002ba Browns Ferry Nuclear Power Stationi Unit 3i Tennessee 0500029b AUTHOR AFFILIATION Tennessee Valley Authority REC I P I ENT*FF I L I ATI ON HWR Prospect Directorate 2

SUBJECT:

Responds to 851007 request for addi info re NUREG-0737'tem II'.K.3.18'Mods to Automatic Depressuri xation Sgs (ADS)Logic." No design basis requirement or increase in safety associated w/requested ADS logic mod.Present ADS adequate.DISTRIBUTION CODE: 104bD COPIES RECEIVED: LTR j ENCL g SIZE: TITLE: OR Submittal:

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i',I 8;i Pt>'7 QQ'y$))/Q A aAAA)')GBB'33 I'RQO)3" 13'P 1J (>TABS"SI;.)>8.3)']AYih HQ>)..i Q I i"~'('l'A H~3 RW'z L0 G i~G1 f)N")()l4l 0 I F v 01 4h C 8 7 RC".'3 I<.~k.HA~1 DA TENNESSEE VALLEY AUTHORITY 5N 157B Lookout Place March 26, 1986 Director of Nuclear Reactor Regulation Attention:

Mr.D.R.Muller, Project Director BWR Project Directorate No.2 Division of Boiling Water Reactor Licensing U.S.Nuclear Regulatory Commission Washington, D.C.20555

Dear Mr.Muller:

In the Matter of the Tennessee Valley Authority Docket Nos.50-2S9 50-260 50-296 By letter from D.B.Vassallo to H.G.Parris dated October 7, 1985, we received a request for additional information regarding NUREG-0737, Item II.K.3.18, Modifications to Automatic Depressurization System Logic, for the Browns Ferry Nuclear Plant.Specifically requested was that.we inform NRC of our plans and schedule for implementing one of the NRC-approved modifications.

We continue to maintain our position that there is no design basis requirement or a significant increase in safety associated with the ADS logic modification requested by NRC.The current ADS initiation logic is designed to mitigate intermediate and small breaks in the primary system boundary, assuming no HPCI injection and taking no credit for operator action.The requested modification appears to go beyond this basis by requiring that operator action also be excluded from other analyses, such as stuck open relief valve with HPCI failure, although it can be shown that time is available for manual depressurization (greater than 10 minutes).It is also not clear that the increase in safety by further assuring a reactor depressurization for certain events outweighs the decrease in safety due to inadvertent actuation in certain other events such as instrument malfunction.

For primary system isolation events with the loss of high pressure makeup systems, the BWR Owners'roup analysis has shown that the operator has at least 30 to 40 minutes to initiate the ADS and prevent excessive fuel cladding heatup.Based on the BWR Owners'roup analysis and an Oak Ridge Laboratory study concerning loss of control air we have concluded that automatic ADS actuation would most likely occur without operator action within about 10 minutes after reactor pressure vessel level decreases to level 1 even for events which do not directly pressurize the drywall.In these events, the drywell becomes indirectly pressurized since reaching level 1 will cause containment isolation and a subsequent heatup and pressurization of the drywell due to the loss of drywell cooling.This heatup and pressurization will most likely result in ADS actuation within about, 10 minutes after the RPV water level decreasos to level 1.8604080229 860326 PDR ADOCK 05000259 P PDR An Equal Opportunity Employer

'N N Director of Nuclear Reactor Regulation March 26, 1986 For small break LOCA events with no high pressure makeup, analyses have shown successful accident mitigation with no operator action fox the first 10 minutes and a complete failure of the ADS logic.Analyses prepared by the General Electric Company for BFN units 1, 2, and 3 examine primary system breaks ranging in size from 0.05 ft through 0.50 ft with a complete loss of the ADS logic function.This analysis is enclosed.These scenarios assume actuation of four main steam relief valves 10 minutes after the break.It can be concluded that with total failure of ADS initiation logic and no operator actions within 10 minutes, adequate core cooling can be maintained with a primary system break equivalent to a stuck open relief valve and no high pressure makeup.The intent of NUREG-0737, Item II.K.3.18, is to provide additional assurance of adequate coxe cooling for transient and accident events which do not produce a high drywell pressuxe signal and are degraded by a loss of all high pressure coolant systems.Based upon our earlier submittals in which reliance was placed on use of symptom-oriented emergency procedure guidelines and with the additional analyses intxoduced in this submittal, TVA concludes that the existing ADS is adequate.Very truly yours, TENNESSEE VALLEY AUTHORITY Enclosure cc (Enclosure):

Mr.R.J.Clax'k U.S.Nuclear Regulatory Commission Browns Ferry Project Manager 7920 Norfolk Avenue Bethesda, Maryland 20814~~R.ridley Manager of icensing U.S.Nuclear Regulatory Commission Region II ATTN: Dr.J.Nelson Grace, Regional Administrator 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 II I II J I II